FLOW BIREFRINGENCE OF FLEXIBLE POLYMER-CHAINS IN STEADY SHEAR-FLOW - A BROWNIAN DYNAMICS SIMULATION

The steady-shear flow birefringence of flexible polymers modeled as Gaussian chains has been studied using Brownian dynamics simulation. The influence of flow rate and chain length on the two important parameters in flow birefringence measurements, the extinction angle chi and the birefringence DELTAn, has been investigated, and the power laws obtained have been compared with theoretical predictions. Hydrodynamic interaction (HI) has been included by means of the Rotne-Prager-Yamakawa tensor, and the simulation results have been compared with the no-HI case. For low shear rates inclusion of HI reduces the influence of flow on DELTAn and tan 2chi, while for high flow rates the chain behaves as in the no-HI case due to the large separation between beads and thereby elimination of flow interaction. For the shear compliance J, we obtain the value 0.29, which is higher than the theoretical value with preaveraged HI (0.20) and lower than that of the free-draining case (0.40), suggesting that preaveraged HI puts a too high weight on the HI contribution. The stress optical coefficient C has also been studied and found to be independent of chain length, shear rate, and HI.